6 replies to this topic

[Steam]

Not an expert at this by any means but I understand the principles.
I have some questions for those who know more than I.
The plugs in my 1275 as follows.
Plugs 1, 2 & 4 have light to mid grey deposits, no brown or tan at all.
Plug 3 seems to have no deposits and electrode looks sort of dry and a bit shiny and black, not carbon though.
Plugs 2 & 3, the porcelain is light brownish.
Plugs 1 & 4 the porcelain is very white and clean.
All four have carbon soot on the steel ring, thread end.
No 3 worries me and the light grey deposits confuse me.

[richmondclassicsnorthwales]

I would be happy with that

[GraemeC]

Its not as easy to read plugs with unleaded fuels - the colorations are not as clear and pronounced as they were with leaded fuel. I suspect this is what is causing the grey deposits.

As above - what you have sounds about right, it may be very slightly lean but if it is running well I wouldn't be to concerned.

[andyapanel]

You would need to worry if they were sooted or oiled. They sound fine.

[Steam]

OK thanks guys. It has a very slight hesitation at cruise.
No 3 being different to the rest was my main worry, any ideas on that?

[cal844]

Check the dashpot oil level, test drive... If that doesn't work try a flat of fuel

[Tornado99]

OK thanks guys. It has a very slight hesitation at cruise.
No 3 being different to the rest was my main worry, any ideas on that?

is this with a single carb? That might contribute to different readings on the plugs as the intake manifold has uneven flow characteristics due to the flow paths needed. Its all a bit of a compromise to make it fit.

If your compression is good, plugs not sooty (rich), black wet. (Oily) or with whitish deposits/signs of electrode erosion (over lean/hot), you are ok.
On classic motorcycles, the rec is to run the bike at full throttle for a bit, then shut off engine without closing throttle to let it idle. This lets you read the plugs from a max fuel flow situation to know how the mixture is. Any time idling will change the reading a lot.

Edited by Tornado99, 12 July 2021 - 04:38 PM.